Recovery of asbestos from asbestos tailings



March 14, 1950 R. E. CROCKETT 2,500,154

RECOVERY OF ASBESTOS; FROM ASBESTOS TAILINGS Filed Sept. 28, 1946ASBESTOS TAILINGS VIOLENT HYDRAULIC 'SORUBBING WET MAGNETIC SEPARATIONSLIME TAILS-GOARSE TAILS-MIDDLINGS CONOENTRATES THICKENER T GRINDING mu.I TABLE SHAKING I I I MAGNETIC SEP. OHROMITE-SERPENTINE -AsaE.Tos(RE-CLEANING) I I RE-TAQLE IF I I may I i I MAGNESIA I I I I ,Lmgmmmmsswoncmmmzs I L VIBRATIN UNDERSIZE OVERSIZE wAsT E THICKENER' I?FILTER MARKET WASTE INVENTOR.

ROBERT E. CROOKETT Patented Mar. 14, 1950 i 2,500,154 I RECOVERY OFASBESTOS FROM ASBESTOS TAILINGS Robert E. Crockett, Montclair, n.1,assignor to H. A. Brassert & Company, New

a corporation of Illinois Application September 28, 1946, Serial No.700,021

v 1 Claim. 1

This invention relates to methods for producing asbestos fibers, and itrelates particularly to methods for recovering asbestos fibers from thetailings produced in asbestos'mining operations. Chrysotile, the mostcommon source of asbestos fibers, occurs in veins in serpentine rockwhich usually is found in formations containing iron, nickel, and chromeores. During the mining of chrysotile, the rock is removed and crushedin order to separate the chrysotile crystals from the rock. Whenchrysotile is separated from the rock, substantial quantities of theasbestos fibers remain attached to the rock and are discarded with therock as a tailing. Despite the fact thatsubstantial quantities ofasbestos are present in the tailings, it has not been feasible oreconomical heretofore to attempt to separate and recover the asbestos.

. One of the principal difliculties encountered in recovering theasbestos fibers from the tailings has been to separate them withoutdeterioration in the quality of the fibers. Such operations as dry orwet grinding of the tailings breaks the fibers into short lengths whichreduce their market value to such an extent that recovery isuneconomical.

An object of the present invention is to provide a method for recoveringasbestos fibers from the tailings resulting from such mining operationsin an economical and simple manner.

A further object of the invention is to provide a method for treatingasbestos-containing tailings to recover the asbestos fibers therefromand sufficient other components of the tailings to render the methodeconomically feasible.

Another object of the present invention is to provide a method fortreating asbestos-containin tailings to recover the asbestos fiberstherein without substantial deterioration in the quality of the fibers.I

Other objects of the invention will become apparent from the followingdescription of a typical method embodying the present invention.

york, N. Y.,

The present invention overcomes the difiiculties of prior attempts torecover the asbestos fibers from the tailings by preliminary grindingfor the reason that the hydraulic scrubbing and agitation of thisinvention does not subject the fibers to sufficiently violent impact tobreak them into shorter lengths. Instead it separates the fiberssubstantially cleanly from the rock, even in cases where the fibers aredisposed in recesses in the rock or are adhered to or grow" out of theore. Therefore, the

method of the present invention permits suband iron industry.

I have discovered that the asbestos fibers in the For a betterunderstanding of the present invention, reference may be had to theaccompanying drawings in which the single figure discloses a typicalfiow sheet of the method embodying the invention.

As illustrated in the drawing, the coarsely ground asbestos tailingswhich comprise a mixture of serpentine rock, chrome, iron, and nickelores, dirt and other materials and asbestos fibers attached to theserpentine rock, is mixed with water and is subjected to a violenthydraulic scrubbing by disposing the mixture in a tank which is providedwith a propeller blade or paddle arrangement that is rotated atrelatively high speed.

The scrubbing operation which may be conducted for a period of /2 to 2hours detaches the asbestos fibers or crystals from the rock andseparates tiny particles of grit, dust, dirt, and other impurities fromthe fibers.

Following the scrubbing operation, the scrubbed material is fed to a wetmagnetic separator of conventional type, such as the Dings-Crockettseparator, which produces a rougher concentrate containing iron, nickel,and some chrome ore. This concentrate may be ground and retreated inanother wet magnetic separator to improve the grade of the iron andnickel ore and to remove some chrome ore and other gangue material. Thisrecleaned concentrate is of value as a source of iron and nickel for usein the iron and steel industry.

The wet magnetic separator will also produce a middling material, aspigot product, a coarse tailing spigot product, and a fine orslimeoverflow.

' amiss delivered to a wet shaking table of a conventional type where achrome ore concentrate, a serpentine rock middling product, and anasbestos fiber tailing are produced.

'I'hechrome concentrate may be cleanedefur tber by retabling andprovides a useful source of chromium. I

,The serpentine rock middling is of little value other than for itsmagnesia content and can be discarded. I

Theasbestostailingcanbepassedtoafurther shaking table where gritparticles are eliminated and a cleaned fiber is produced.

"The slime tailing product from the magnetic separator can, if desired,be sent to thickeners of the Dorr type where excess water is removed.

However, the fibers and other material contained in the slime tailingproduct are not very valuable and can be delivered to waste instead ofthickening, if desired.

In order to classify the asbestos fiber product produced by thetablingoperations, it is passed to a vibrating screen of a very fine mesh, for,example, 65 or 100 mesh, or even finer, where the fibers arerfurtherscrubbed and any fine fibers or very short fibers will be removed. Thefibers remaining on top of the screen will be discharged satisfactoryrecovery of asbestos fibers of a com-- mercially valuable length fromthe. tailings and inasmuch as the method permits large quantities of thetailing to be handled with a small amount of equipment and expenditureof power, the fibers can be recovered suificiently economically tojustify the treatment of the tailings. The cost or a recovery of chrome,nickel, and iron ores'whicb" are of commercial value.

It will be understood that the procedure followed subsequent to thehydraulic scrubbing operation is susceptible to considerable variationas indicated above depending inss being treated. 2

, Therefore, the process described above should be considered asillustrative and not as limiting the scope of the following claim. 1

I claim:

A method of recovering asbestos from taiiings of asbestos miningoperations, said tailings containing serpentine rook, iron, nickel andchrome ores and asbestos fibers attached to said rock, comprising mixingof said tailings with water, subjecting the tailings to violenthydraulic scrubbing to free the fibers from other components of saidtailings, magnetically concentrating and separating said iron and nickelores from said mixture, wet tabling said mixtur to separate it into achrome concentrate, a serpentine rock middling and a substantially cleanasbestos fiber tailing, and then classifyingsaid tailing to separate thefine fibers from the longer fibers. 1

ROBERT E. cRocKE'rr. i

REFE RENCES CITED UNITED STATES PATENTS Number' Name Date 85 1,338,613Cilley Apr. 27, 1920 1,632,620 .Nanfeldt June 14, 1927 1,684,365 DolbearSept. 11, 1928 1,684,366 Dolbear Sept. 11, 1928 1,714,438 Rose May 21,1929 0 1,741,869 Mett Dec. 31, 1929 2,291,042 Kennedy July 28, 19422,386,713 Pharo Oct. 9, 1945 OTHER REFERENCES Bureau of Mines R. 1.,4079, June 1947 (26 production of the fiber is reduced further by'thepages),

upon the type of tail-

